[yocto] Kernel configuration fragments and defconfig from kernel source tree, not meta layer file

[Alex J Lennon]

Hi,

I've been looking into a request to have Yocto kernel configuration
fragment support in meta-raspberrypi with a defconfig which is pulled
from the kernel source tree for the configured machine.

My understanding is that Yocto expects the defconfig file to be supplied
in the meta-layer and then configured with SRC_URI += "file://defconfig"

We'd prefer not to maintain copies of defconfigs, instead using the true
default configuration from the kernel tree and allowing users to add
their own .cfg fragments to the SRC_URI via, say, .bbappends.

It's easy enough to _prepend() a function to copy the appropriate
defconfig from the kernel source to the working directory, but I am
having a problem as do_patch() in kernel-yocto.bbclass seems to require
a defconfig file from the layer itself via use of SRC_URI in find_sccs().

Any thoughts? Thanks,

Alex